This invention relates to a lightning arrester system for a power transmission line for preventing damage of an insulator string supporting the power transmission line on a tower by a lightning stroke.
A prior art lightning arrester system of the aforementioned type this kind is disclosed in, for example, JP-A-61-260506 and is shown in FIG. 1 wherein, a suspension insulator string 32; consisting of a series of a plurality of suspension insulators, is suspended at its upper end from the bottom of an arm structure 4 of a tower and supports a power transmission line 3 at its lower end. A lightning isolator unit 10 is fixed at its upper end to a free end 33A of a fitting 33 fixed at the other end to the arm structure 4 of the tower, and a series gap 37 is formed between a discharge electrode 38, fixed to the lower end of the lightning isolator unit 10, and a discharge electrode 36 fixed to the suspension insulator string 32 on the side of the power transmission line 3.
Thus, in the prior art lightning system arrester, the series connection of the lightning isolator unit 10 and the series gap 37 is arranged in an electrically parallel relationship to the suspension insulator string 32. Therefore, when a surge due to a lightning stroke is applied to the power transmission line 3, discharge occurs across the series gap 37, and the lightning isolator unit 10 interrupts the flow current having a small current value, so that flashover across the suspension insulator string 32 is prevented.
However, in the prior art lightning arrester, the lightning isolator unit 10 is directly connected at its grounded side by the fitting 33 to the tower arm structure 4 having the ground potential, and the grounded side of the lightning isolator unit 10 and the fitting 33 have the same ground potential. Because of the above arrangement, the protective effect of the lightning isolator unit 10 from the viewpoints of confirmation of the operation of the lightning isolator unit 10, indication of failure of the lightning isolator unit 10 in the event of occurrence of an accident, etc. could not be fully determined grasped.